Fiber optic sensor arrays of a time division multiplexed (“TDM”) system are often used to measure a change in an external parameter, for example, acoustic vibration, fluid pressure variations, acceleration, and magnetic field intensity. The fiber optic sensor array employs a phase generated carrier with a period T to measure the change in the external parameter at a given sampling rate. The fiber optic sensor array converts a time-varying phase angle associated with the external parameter to an amplitude variation on an output pulse of light.
The phase angle is measured through various demodulation techniques of the output pulse. Typical demodulation techniques employ a quadrature component Q and an in-phase component I of the output pulse. The quadrature component Q corresponds to a sine of the phase angle, and the in-phase component I corresponds to a cosine of the phase angle. An arctangent of the ratio Q/I is equal to the phase angle. The magnitude of the change in the external parameter can then be calculated from the change in the phase angle.
Calculation of the quadrature component Q and the in-phase component I requires multiple samples of the output pulse at specific intervals of the phase generated carrier. The phase generated carrier comprises a period that is significantly longer than a period of the output pulse. The longer period of the phase generated carrier requires the samples to span several output pulses to obtain each required interval of the phase generated carrier. It is desirable to increase the rate of calculation of the phase angle to promote an increase in throughput. For a constant sampling rate, the number of required samples must be reduced to increase the rate of calculation of the phase angle.
Thus, a need exists for reduced numbers of required samples for demodulation techniques of fiber optic sensor arrays that employ phase generated carriers.